text: # -*- test-case-name: twisted.conch.test.test_userauth -*-
  # Copyright (c) Twisted Matrix Laboratories.
  # See LICENSE for details.
  
  """
  Implementation of the ssh-userauth service.
  Currently implemented authentication types are public-key and password.
  
  Maintainer: Paul Swartz
  """
  
  from __future__ import absolute_import, division
  
  import struct
  
  from twisted.conch import error, interfaces
  from twisted.conch.ssh import keys, transport, service
  from twisted.conch.ssh.common import NS, getNS
  from twisted.cred import credentials
  from twisted.cred.error import UnauthorizedLogin
  from twisted.internet import defer, reactor
  from twisted.python import failure, log
  from twisted.python.compat import nativeString, _bytesChr as chr
  
  
  
  class SSHUserAuthServer(service.SSHService):
      """
      A service implementing the server side of the 'ssh-userauth' service.  It
      is used to authenticate the user on the other side as being able to access
      this server.
  
      @ivar name: the name of this service: 'ssh-userauth'
      @type name: L{bytes}
      @ivar authenticatedWith: a list of authentication methods that have
          already been used.
      @type authenticatedWith: L{list}
      @ivar loginTimeout: the number of seconds we wait before disconnecting
          the user for taking too long to authenticate
      @type loginTimeout: L{int}
      @ivar attemptsBeforeDisconnect: the number of failed login attempts we
          allow before disconnecting.
      @type attemptsBeforeDisconnect: L{int}
      @ivar loginAttempts: the number of login attempts that have been made
      @type loginAttempts: L{int}
      @ivar passwordDelay: the number of seconds to delay when the user gives
          an incorrect password
      @type passwordDelay: L{int}
      @ivar interfaceToMethod: a L{dict} mapping credential interfaces to
          authentication methods.  The server checks to see which of the
          cred interfaces have checkers and tells the client that those methods
          are valid for authentication.
      @type interfaceToMethod: L{dict}
      @ivar supportedAuthentications: A list of the supported authentication
          methods.
      @type supportedAuthentications: L{list} of L{bytes}
      @ivar user: the last username the client tried to authenticate with
      @type user: L{bytes}
      @ivar method: the current authentication method
      @type method: L{bytes}
      @ivar nextService: the service the user wants started after authentication
          has been completed.
      @type nextService: L{bytes}
      @ivar portal: the L{twisted.cred.portal.Portal} we are using for
          authentication
      @type portal: L{twisted.cred.portal.Portal}
      @ivar clock: an object with a callLater method.  Stubbed out for testing.
      """
  
      name = b'ssh-userauth'
      loginTimeout = 10 * 60 * 60
      # 10 minutes before we disconnect them
      attemptsBeforeDisconnect = 20
      # 20 login attempts before a disconnect
      passwordDelay = 1 # number of seconds to delay on a failed password
      clock = reactor
      interfaceToMethod = {
          credentials.ISSHPrivateKey : b'publickey',
          credentials.IUsernamePassword : b'password',
      }
  
  
      def serviceStarted(self):
          """
          Called when the userauth service is started.  Set up instance
          variables, check if we should allow password authentication (only
          allow if the outgoing connection is encrypted) and set up a login
          timeout.
          """
          self.authenticatedWith = []
          self.loginAttempts = 0
          self.user = None
          self.nextService = None
          self.portal = self.transport.factory.portal
  
          self.supportedAuthentications = []
          for i in self.portal.listCredentialsInterfaces():
              if i in self.interfaceToMethod:
                  self.supportedAuthentications.append(self.interfaceToMethod[i])
  
          if not self.transport.isEncrypted('in'):
              # don't let us transport password in plaintext
              if b'password' in self.supportedAuthentications:
                  self.supportedAuthentications.remove(b'password')
          self._cancelLoginTimeout = self.clock.callLater(
              self.loginTimeout,
              self.timeoutAuthentication)
  
  
      def serviceStopped(self):
          """
          Called when the userauth service is stopped.  Cancel the login timeout
          if it's still going.
          """
          if self._cancelLoginTimeout:
              self._cancelLoginTimeout.cancel()
              self._cancelLoginTimeout = None
  
  
      def timeoutAuthentication(self):
          """
          Called when the user has timed out on authentication.  Disconnect
          with a DISCONNECT_NO_MORE_AUTH_METHODS_AVAILABLE message.
          """
          self._cancelLoginTimeout = None
          self.transport.sendDisconnect(
              transport.DISCONNECT_NO_MORE_AUTH_METHODS_AVAILABLE,
              b'you took too long')
  
  
      def tryAuth(self, kind, user, data):
          """
          Try to authenticate the user with the given method.  Dispatches to a
          auth_* method.
  
          @param kind: the authentication method to try.
          @type kind: L{bytes}
          @param user: the username the client is authenticating with.
          @type user: L{bytes}
          @param data: authentication specific data sent by the client.
          @type data: L{bytes}
          @return: A Deferred called back if the method succeeded, or erred back
              if it failed.
          @rtype: C{defer.Deferred}
          """
          log.msg('%r trying auth %r' % (user, kind))
          if kind not in self.supportedAuthentications:
              return defer.fail(
                      error.ConchError('unsupported authentication, failing'))
          kind = nativeString(kind.replace(b'-', b'_'))
          f = getattr(self, 'auth_%s' % (kind,), None)
          if f:
              ret = f(data)
              if not ret:
                  return defer.fail(
                          error.ConchError(
                              '%s return None instead of a Deferred'
                              % (kind, )))
              else:
                  return ret
          return defer.fail(error.ConchError('bad auth type: %s' % (kind,)))
  
  
      def ssh_USERAUTH_REQUEST(self, packet):
          """
          The client has requested authentication.  Payload::
              string user
              string next service
              string method
              <authentication specific data>
  
          @type packet: L{bytes}
          """
          user, nextService, method, rest = getNS(packet, 3)
          if user != self.user or nextService != self.nextService:
              self.authenticatedWith = [] # clear auth state
          self.user = user
          self.nextService = nextService
          self.method = method
          d = self.tryAuth(method, user, rest)
          if not d:
              self._ebBadAuth(
                  failure.Failure(error.ConchError('auth returned none')))
              return
          d.addCallback(self._cbFinishedAuth)
          d.addErrback(self._ebMaybeBadAuth)
          d.addErrback(self._ebBadAuth)
          return d
  
  
      def _cbFinishedAuth(self, result):
          """
          The callback when user has successfully been authenticated.  For a
          description of the arguments, see L{twisted.cred.portal.Portal.login}.
          We start the service requested by the user.
          """
          (interface, avatar, logout) = result
          self.transport.avatar = avatar
          self.transport.logoutFunction = logout
          service = self.transport.factory.getService(self.transport,
                  self.nextService)
          if not service:
              raise error.ConchError('could not get next service: %s'
                                    % self.nextService)
          log.msg('%r authenticated with %r' % (self.user, self.method))
          self.transport.sendPacket(MSG_USERAUTH_SUCCESS, b'')
          self.transport.setService(service())
  
  
      def _ebMaybeBadAuth(self, reason):
          """
          An intermediate errback.  If the reason is
          error.NotEnoughAuthentication, we send a MSG_USERAUTH_FAILURE, but
          with the partial success indicator set.
  
          @type reason: L{twisted.python.failure.Failure}
          """
          reason.trap(error.NotEnoughAuthentication)
          self.transport.sendPacket(MSG_USERAUTH_FAILURE,
                  NS(b','.join(self.supportedAuthentications)) + b'\xff')
  
  
      def _ebBadAuth(self, reason):
          """
          The final errback in the authentication chain.  If the reason is
          error.IgnoreAuthentication, we simply return; the authentication
          method has sent its own response.  Otherwise, send a failure message
          and (if the method is not 'none') increment the number of login
          attempts.
  
          @type reason: L{twisted.python.failure.Failure}
          """
          if reason.check(error.IgnoreAuthentication):
              return
          if self.method != b'none':
              log.msg('%r failed auth %r' % (self.user, self.method))
              if reason.check(UnauthorizedLogin):
                  log.msg('unauthorized login: %s' % reason.getErrorMessage())
              elif reason.check(error.ConchError):
                  log.msg('reason: %s' % reason.getErrorMessage())
              else:
                  log.msg(reason.getTraceback())
              self.loginAttempts += 1
              if self.loginAttempts > self.attemptsBeforeDisconnect:
                  self.transport.sendDisconnect(
                          transport.DISCONNECT_NO_MORE_AUTH_METHODS_AVAILABLE,
                          b'too many bad auths')
                  return
          self.transport.sendPacket(
                  MSG_USERAUTH_FAILURE,
                  NS(b','.join(self.supportedAuthentications)) + b'\x00')
  
  
      def auth_publickey(self, packet):
          """
          Public key authentication.  Payload::
              byte has signature
              string algorithm name
              string key blob
              [string signature] (if has signature is True)
  
          Create a SSHPublicKey credential and verify it using our portal.
          """
          hasSig = ord(packet[0:1])
          algName, blob, rest = getNS(packet[1:], 2)
          pubKey = keys.Key.fromString(blob)
          signature = hasSig and getNS(rest)[0] or None
          if hasSig:
              b = (NS(self.transport.sessionID) + chr(MSG_USERAUTH_REQUEST) +
                  NS(self.user) + NS(self.nextService) + NS(b'publickey') +
                  chr(hasSig) +  NS(pubKey.sshType()) + NS(blob))
              c = credentials.SSHPrivateKey(self.user, algName, blob, b,
                      signature)
              return self.portal.login(c, None, interfaces.IConchUser)
          else:
              c = credentials.SSHPrivateKey(self.user, algName, blob, None, None)
              return self.portal.login(c, None,
                      interfaces.IConchUser).addErrback(self._ebCheckKey,
                              packet[1:])
  
  
      def _ebCheckKey(self, reason, packet):
          """
          Called back if the user did not sent a signature.  If reason is
          error.ValidPublicKey then this key is valid for the user to
          authenticate with.  Send MSG_USERAUTH_PK_OK.
          """
          reason.trap(error.ValidPublicKey)
          # if we make it here, it means that the publickey is valid
          self.transport.sendPacket(MSG_USERAUTH_PK_OK, packet)
          return failure.Failure(error.IgnoreAuthentication())
  
  
      def auth_password(self, packet):
          """
          Password authentication.  Payload::
              string password
  
          Make a UsernamePassword credential and verify it with our portal.
          """
          password = getNS(packet[1:])[0]
          c = credentials.UsernamePassword(self.user, password)
          return self.portal.login(c, None, interfaces.IConchUser).addErrback(
                                                          self._ebPassword)
  
  
      def _ebPassword(self, f):
          """
          If the password is invalid, wait before sending the failure in order
          to delay brute-force password guessing.
          """
          d = defer.Deferred()
          self.clock.callLater(self.passwordDelay, d.callback, f)
          return d
  
  
  
  class SSHUserAuthClient(service.SSHService):
      """
      A service implementing the client side of 'ssh-userauth'.
  
      This service will try all authentication methods provided by the server,
      making callbacks for more information when necessary.
  
      @ivar name: the name of this service: 'ssh-userauth'
      @type name: L{str}
      @ivar preferredOrder: a list of authentication methods that should be used
          first, in order of preference, if supported by the server
      @type preferredOrder: L{list}
      @ivar user: the name of the user to authenticate as
      @type user: L{bytes}
      @ivar instance: the service to start after authentication has finished
      @type instance: L{service.SSHService}
      @ivar authenticatedWith: a list of strings of authentication methods we've tried
      @type authenticatedWith: L{list} of L{bytes}
      @ivar triedPublicKeys: a list of public key objects that we've tried to
          authenticate with
      @type triedPublicKeys: L{list} of L{Key}
      @ivar lastPublicKey: the last public key object we've tried to authenticate
          with
      @type lastPublicKey: L{Key}
      """
  
      name = b'ssh-userauth'
      preferredOrder = [b'publickey', b'password', b'keyboard-interactive']
  
  
      def __init__(self, user, instance):
          self.user = user
          self.instance = instance
  
  
      def serviceStarted(self):
          self.authenticatedWith = []
          self.triedPublicKeys = []
          self.lastPublicKey = None
          self.askForAuth(b'none', b'')
  
  
      def askForAuth(self, kind, extraData):
          """
          Send a MSG_USERAUTH_REQUEST.
  
          @param kind: the authentication method to try.
          @type kind: L{bytes}
          @param extraData: method-specific data to go in the packet
          @type extraData: L{bytes}
          """
          self.lastAuth = kind
          self.transport.sendPacket(MSG_USERAUTH_REQUEST, NS(self.user) +
                  NS(self.instance.name) + NS(kind) + extraData)
  
  
      def tryAuth(self, kind):
          """
          Dispatch to an authentication method.
  
          @param kind: the authentication method
          @type kind: L{bytes}
          """
          kind = nativeString(kind.replace(b'-', b'_'))
          log.msg('trying to auth with %s' % (kind,))
          f = getattr(self,'auth_%s' % (kind,), None)
          if f:
              return f()
  
  
      def _ebAuth(self, ignored, *args):
          """
          Generic callback for a failed authentication attempt.  Respond by
          asking for the list of accepted methods (the 'none' method)
          """
          self.askForAuth(b'none', b'')
  
  
      def ssh_USERAUTH_SUCCESS(self, packet):
          """
          We received a MSG_USERAUTH_SUCCESS.  The server has accepted our
          authentication, so start the next service.
          """
          self.transport.setService(self.instance)
  
  
      def ssh_USERAUTH_FAILURE(self, packet):
          """
          We received a MSG_USERAUTH_FAILURE.  Payload::
              string methods
              byte partial success
  
          If partial success is C{True}, then the previous method succeeded but is
          not sufficient for authentication. C{methods} is a comma-separated list
          of accepted authentication methods.
  
          We sort the list of methods by their position in C{self.preferredOrder},
          removing methods that have already succeeded. We then call
          C{self.tryAuth} with the most preferred method.
  
          @param packet: the C{MSG_USERAUTH_FAILURE} payload.
          @type packet: L{bytes}
  
          @return: a L{defer.Deferred} that will be callbacked with L{None} as
              soon as all authentication methods have been tried, or L{None} if no
              more authentication methods are available.
          @rtype: C{defer.Deferred} or L{None}
          """
          canContinue, partial = getNS(packet)
          partial = ord(partial)
          if partial:
              self.authenticatedWith.append(self.lastAuth)
  
          def orderByPreference(meth):
              """
              Invoked once per authentication method in order to extract a
              comparison key which is then used for sorting.
  
              @param meth: the authentication method.
              @type meth: L{bytes}
  
              @return: the comparison key for C{meth}.
              @rtype: L{int}
              """
              if meth in self.preferredOrder:
                  return self.preferredOrder.index(meth)
              else:
                  # put the element at the end of the list.
                  return len(self.preferredOrder)
  
          canContinue = sorted([meth for meth in canContinue.split(b',')
                                if meth not in self.authenticatedWith],
                               key=orderByPreference)
  
          log.msg('can continue with: %s' % canContinue)
          return self._cbUserauthFailure(None, iter(canContinue))
  
  
      def _cbUserauthFailure(self, result, iterator):
          if result:
              return
          try:
              method = next(iterator)
          except StopIteration:
              self.transport.sendDisconnect(
                  transport.DISCONNECT_NO_MORE_AUTH_METHODS_AVAILABLE,
                  b'no more authentication methods available')
          else:
              d = defer.maybeDeferred(self.tryAuth, method)
              d.addCallback(self._cbUserauthFailure, iterator)
              return d
  
  
      def ssh_USERAUTH_PK_OK(self, packet):
          """
          This message (number 60) can mean several different messages depending
          on the current authentication type.  We dispatch to individual methods
          in order to handle this request.
          """
          func = getattr(self, 'ssh_USERAUTH_PK_OK_%s' %
                         nativeString(self.lastAuth.replace(b'-', b'_')), None)
          if func is not None:
              return func(packet)
          else:
              self.askForAuth(b'none', b'')
  
  
      def ssh_USERAUTH_PK_OK_publickey(self, packet):
          """
          This is MSG_USERAUTH_PK.  Our public key is valid, so we create a
          signature and try to authenticate with it.
          """
          publicKey = self.lastPublicKey
          b = (NS(self.transport.sessionID) + chr(MSG_USERAUTH_REQUEST) +
               NS(self.user) + NS(self.instance.name) + NS(b'publickey') +
               b'\x01' + NS(publicKey.sshType()) + NS(publicKey.blob()))
          d  = self.signData(publicKey, b)
          if not d:
              self.askForAuth(b'none', b'')
              # this will fail, we'll move on
              return
          d.addCallback(self._cbSignedData)
          d.addErrback(self._ebAuth)
  
  
      def ssh_USERAUTH_PK_OK_password(self, packet):
          """
          This is MSG_USERAUTH_PASSWD_CHANGEREQ.  The password given has expired.
          We ask for an old password and a new password, then send both back to
          the server.
          """
          prompt, language, rest = getNS(packet, 2)
          self._oldPass = self._newPass = None
          d = self.getPassword(b'Old Password: ')
          d = d.addCallbacks(self._setOldPass, self._ebAuth)
          d.addCallback(lambda ignored: self.getPassword(prompt))
          d.addCallbacks(self._setNewPass, self._ebAuth)
  
  
      def ssh_USERAUTH_PK_OK_keyboard_interactive(self, packet):
          """
          This is MSG_USERAUTH_INFO_RESPONSE.  The server has sent us the
          questions it wants us to answer, so we ask the user and sent the
          responses.
          """
          name, instruction, lang, data = getNS(packet, 3)
          numPrompts = struct.unpack('!L', data[:4])[0]
          data = data[4:]
          prompts = []
          for i in range(numPrompts):
              prompt, data = getNS(data)
              echo = bool(ord(data[0:1]))
              data = data[1:]
              prompts.append((prompt, echo))
          d = self.getGenericAnswers(name, instruction, prompts)
          d.addCallback(self._cbGenericAnswers)
          d.addErrback(self._ebAuth)
  
  
      def _cbSignedData(self, signedData):
          """
          Called back out of self.signData with the signed data.  Send the
          authentication request with the signature.
  
          @param signedData: the data signed by the user's private key.
          @type signedData: L{bytes}
          """
          publicKey = self.lastPublicKey
          self.askForAuth(b'publickey', b'\x01' + NS(publicKey.sshType()) +
                  NS(publicKey.blob()) + NS(signedData))
  
  
      def _setOldPass(self, op):
          """
          Called back when we are choosing a new password.  Simply store the old
          password for now.
  
          @param op: the old password as entered by the user
          @type op: L{bytes}
          """
          self._oldPass = op
  
  
      def _setNewPass(self, np):
          """
          Called back when we are choosing a new password.  Get the old password
          and send the authentication message with both.
  
          @param np: the new password as entered by the user
          @type np: L{bytes}
          """
          op = self._oldPass
          self._oldPass = None
          self.askForAuth(b'password', b'\xff' + NS(op) + NS(np))
  
  
      def _cbGenericAnswers(self, responses):
          """
          Called back when we are finished answering keyboard-interactive
          questions.  Send the info back to the server in a
          MSG_USERAUTH_INFO_RESPONSE.
  
          @param responses: a list of L{bytes} responses
          @type responses: L{list}
          """
          data = struct.pack('!L', len(responses))
          for r in responses:
              data += NS(r.encode('UTF8'))
          self.transport.sendPacket(MSG_USERAUTH_INFO_RESPONSE, data)
  
  
      def auth_publickey(self):
          """
          Try to authenticate with a public key.  Ask the user for a public key;
          if the user has one, send the request to the server and return True.
          Otherwise, return False.
  
          @rtype: L{bool}
          """
          d = defer.maybeDeferred(self.getPublicKey)
          d.addBoth(self._cbGetPublicKey)
          return d
  
  
      def _cbGetPublicKey(self, publicKey):
          if not isinstance(publicKey, keys.Key): # failure or None
              publicKey = None
          if publicKey is not None:
              self.lastPublicKey = publicKey
              self.triedPublicKeys.append(publicKey)
              log.msg('using key of type %s' % publicKey.type())
              self.askForAuth(b'publickey', b'\x00' + NS(publicKey.sshType()) +
                              NS(publicKey.blob()))
              return True
          else:
              return False
  
  
      def auth_password(self):
          """
          Try to authenticate with a password.  Ask the user for a password.
          If the user will return a password, return True.  Otherwise, return
          False.
  
          @rtype: L{bool}
          """
          d = self.getPassword()
          if d:
              d.addCallbacks(self._cbPassword, self._ebAuth)
              return True
          else: # returned None, don't do password auth
              return False
  
  
      def auth_keyboard_interactive(self):
          """
          Try to authenticate with keyboard-interactive authentication.  Send
          the request to the server and return True.
  
          @rtype: L{bool}
          """
          log.msg('authing with keyboard-interactive')
          self.askForAuth(b'keyboard-interactive', NS(b'') + NS(b''))
          return True
  
  
      def _cbPassword(self, password):
          """
          Called back when the user gives a password.  Send the request to the
          server.
  
          @param password: the password the user entered
          @type password: L{bytes}
          """
          self.askForAuth(b'password', b'\x00' + NS(password))
  
  
      def signData(self, publicKey, signData):
          """
          Sign the given data with the given public key.
  
          By default, this will call getPrivateKey to get the private key,
          then sign the data using Key.sign().
  
          This method is factored out so that it can be overridden to use
          alternate methods, such as a key agent.
  
          @param publicKey: The public key object returned from L{getPublicKey}
          @type publicKey: L{keys.Key}
  
          @param signData: the data to be signed by the private key.
          @type signData: L{bytes}
          @return: a Deferred that's called back with the signature
          @rtype: L{defer.Deferred}
          """
          key = self.getPrivateKey()
          if not key:
              return
          return key.addCallback(self._cbSignData, signData)
  
  
      def _cbSignData(self, privateKey, signData):
          """
          Called back when the private key is returned.  Sign the data and
          return the signature.
  
          @param privateKey: the private key object
          @type publicKey: L{keys.Key}
          @param signData: the data to be signed by the private key.
          @type signData: L{bytes}
          @return: the signature
          @rtype: L{bytes}
          """
          return privateKey.sign(signData)
  
  
      def getPublicKey(self):
          """
          Return a public key for the user.  If no more public keys are
          available, return L{None}.
  
          This implementation always returns L{None}.  Override it in a
          subclass to actually find and return a public key object.
  
          @rtype: L{Key} or L{None}
          """
          return None
  
  
      def getPrivateKey(self):
          """
          Return a L{Deferred} that will be called back with the private key
          object corresponding to the last public key from getPublicKey().
          If the private key is not available, errback on the Deferred.
  
          @rtype: L{Deferred} called back with L{Key}
          """
          return defer.fail(NotImplementedError())
  
  
      def getPassword(self, prompt = None):
          """
          Return a L{Deferred} that will be called back with a password.
          prompt is a string to display for the password, or None for a generic
          'user@hostname's password: '.
  
          @type prompt: L{bytes}/L{None}
          @rtype: L{defer.Deferred}
          """
          return defer.fail(NotImplementedError())
  
  
      def getGenericAnswers(self, name, instruction, prompts):
          """
          Returns a L{Deferred} with the responses to the promopts.
  
          @param name: The name of the authentication currently in progress.
          @param instruction: Describes what the authentication wants.
          @param prompts: A list of (prompt, echo) pairs, where prompt is a
          string to display and echo is a boolean indicating whether the
          user's response should be echoed as they type it.
          """
          return defer.fail(NotImplementedError())
  
  
  MSG_USERAUTH_REQUEST          = 50
  MSG_USERAUTH_FAILURE          = 51
  MSG_USERAUTH_SUCCESS          = 52
  MSG_USERAUTH_BANNER           = 53
  MSG_USERAUTH_INFO_RESPONSE    = 61
  MSG_USERAUTH_PK_OK            = 60
  
  messages = {}
  for k, v in list(locals().items()):
      if k[:4] == 'MSG_':
          messages[v] = k
  
  SSHUserAuthServer.protocolMessages = messages
  SSHUserAuthClient.protocolMessages = messages
  del messages
  del v
  
  # Doubles, not included in the protocols' mappings
  MSG_USERAUTH_PASSWD_CHANGEREQ = 60
  MSG_USERAUTH_INFO_REQUEST     = 60
  